1. Field of the Invention
The present invention relates to a method for producing a nanostructured non-oxide ceramic material, preferably a high temperature SiCN and/or SiC material, using block copolymers as structure directing agents and polymer derived ceramic (PDC) precursors.
2. Description of Related Art
Despite some successes with methods ranging from colloidal templating to surfactant and block copolymer self-assembly, controlling the structure of ceramic materials at the nanometer length scale remains a challenge. Block copolymer self-assembly is particularly interesting due to the ability to form a variety of different mesophases in the bulk with periodicity in the tens of nanometer regime. As early as 1995, it was demonstrated that their self-assembly character can be employed to direct the structure of silica into mesoporous materials prepared from silicon alkoxides like tetraethylorthosilicate, TEOS. Before this discovery, the common way to produce nanostructures of ceramic materials was based on ionic surfactant systems with the Mobile Composition of Matter, MCM, type materials. Using block copolymers to generate structured silica had the advantage over surfactant based approaches to increase the accessible length scale of these structures by about an order of magnitude. Subsequent research on different block copolymer systems demonstrated the versatility of these materials to mesostructure a variety of different inorganic systems, albeit these were primarily metal oxide systems.
For many applications it is advantageous to move away from oxide structures towards high temperature stable and mechanically robust SiCN and SiC materials. Of particular interest are ceramic materials derived from polymer precursors, so called polymer derived ceramics (PDCs). A prototypical high temperature PDC oligomer/polymer precursor is a silazane commercially known as ‘Ceraset’. Ceraset is a ureamethylvinylsilazane that can be further polymerized to form a polysilazane used in a variety of applications ranging from microelectromechanical devices (MEMS), coatings, and bulk SiCN ceramics. Recently the mechanical properties of bulk ceramics derived from this silazane were characterized. The SiCN ceramic prepared from Ceraset is an extremely stiff ceramic that when heated to temperatures greater than 1500° C. forms SiC with ˜90% crystallinity.